The appearance of different gases dissolved in oil is normally an undesired event since the gases may influence the electrical and chemical properties of the oil. By analysis of gases appearing, it is possible to find out what kind of gas is present in the oil and the concentration of the different gases. With knowledge of which gases appear in the oil, it is also normally possible to draw conclusions as to the reason for the gas formed. It is well known that when hydrogen gas appears in oil which surrounds electrical components, for example a transformer immersed in an oil-filled tank, this is a very clear sign of the occurrence of electrical discharges in the transformer or that there is a local, considerable increase of the temperature of some part of the transformer. In the latter case, also other characteristic gases are formed such as ethylene, etc. The formation of hydrogen gas takes place practically immediately after the occurrence of a discharge. In case of local so-called hot spots, the gas formation takes place in a more continuous manner in quantity depending on the temperature at the site of the fault.
The present invention relates to a method and a device for continuously monitoring gas dissolved in oil. The method will be described for application when monitoring gas dissolved in the oil of transformers but the method can also be used in other applications.